The invention concerns a single-use filter housing of the type to be used in pressure filtration systems.
Single use filter units, including a single-use filter element contained within a single-use housing form part of the present state of art and are being employed in various fields of application, for example for medical and pharmaceutical purposes, in connection with environmental protection services and in laboratory operations. Such units are being used primarily in cases where relatively small quantities of fluid at a highest degree of purity are needed. These filtering units, which include the housing, are termed "single-use" because they are used only one time before being discarded.
The single-use filter units with which the present invention is concerned are designed for a pressure filtration operation. The fluid to be filtered, either a liquid or a gas, is introduced under pressure onto the filter surface. The pressure usually ranges from 1 to 10 bar. These pressures are necessary in order to attain a sufficiently speedy filtration because the filter elements being utilized are normally diaphragm filters with a relatively low filtering speed. As a rule, it can be stated that the higher the filtration pressure, the shorter will be the time required for the filtering of a specific volume.
The single-use filters of the type being discussed here must be mass-produced at very low cost since they will be discarded after a single-use. Inexpensive material and economy of construction will therefore limit the magnitude of filtration pressure to which such single-use filters can be subjected. The upper pressure limits for the filter housings, usually comprising welded-together upper and lower parts, formed of synthetic material, are approximately 15 bar. However, single-use filter elements which are being used at the present time can be subjected only to filtration pressures in the neighborhood of 1 bar because the filter will tear under the influence of higher pressures of flow at which the medium to be filtered is being forced into the filter housing by way of a central charging duct.
A similar problem exists in the case of the large pressure filtration units made of steel which are costly, consist of many components and are designed for a use extending over several years. The problem was solved in the case of such units by the use of a special structural component which holds the filter down at the filter support, the so-called back-pressure screen. This backpressure screen can be attached to the lower or the upper portion of the filter housing in such manner that it can be easily disengaged and removed. The attachment is accomplished in that manner that the downward facing internal surface of the upper housing part remains unobstructed. A so-called baffle plate is bolted by way of spacers to this freely available internal surface of the upper part. This baffle plate deflects radially the flow entering the filter housing axially under pressure, thus preventing the entering flow from striking the filter directly and vertically.
Such structural design which is rather costly cannot be used in the case of the single-use filters which are mass-produced and discarded after one single application. There are known single-use filters of the type being discussed which are constructed without a backpressure screen and baffle plate where the filter diaphragm is welded peripherally between the two housing halves. It was found, however, in the case of single-use filters so constructed that due to the lack of a backpressure screen, even minor filtration pressure fluctuations will cause the filter diaphragm to rise from the filter support so that it will have the tendency to tear. Furthermore, such filters will not allow a filtering in reverse direction, for example when drawing in an injection solution into a syringe from a storage container.
One type of single-use filter housing represents a significant improvement in comparison with the known arrangements. The bottom side of the upper housing part is equipped with radially extending ribs, the lower edges of which being located, after assembly of the single use filter, either directly at or at least immediately adjacent the upper filter surface, which normally constitutes the diaphragm surface. These ribs, which form one single piece with the upper part of the filter housing will hold the filter down at the filter support, thus essentially performing the function of the backpressure screen employed in the case of the large pressure filtration units. The ribs usually number from eight to twelve. This specific design and arrangement of the holding-down ribs prevents, however, the customary placement of the baffle plate above the backpressure screen. The known single-use filter housings, representing the present state of art, are provided therefore with a charging duct which is freely open directly above the filter element surface. As a result thereof, and as explained above, the standard single-use filter housings can be loaded by only 10% of the desired filtration pressure, even though the desired pressure could be absorbed by even the most inexpensively manufactured housing.
It is, therefore, an object of the invention to improve the standard single-use filter housings so that it will become possible, without any appreciable increase in production costs, to manufacture single-use filter units that can be subjected to the maximum pressure able to be sustained by the housing and which will also operate in a reliable manner during operations involving the drawing-in of the fluid.
It is another object of the present invention to provide a single-use filter housing whose upper part is of one-piece molded construction and comprises filter hold-down ribs and a baffle disk which prevents the direct impingement of vertically entering fluid against the filter element.